The advantage of optomechanical systems is that subsystems of different frequencies can be entangled by interaction with mechanical oscillators. In this paper, the entanglement of two longitudinal modes entangled by light-force coupling under special conditions is studied. The influence of filter function and input-output relation is considered in covariance matrix. The results show that there is still steady-state entanglement between the two optical modes of the output, and larger entanglement can be obtained by optimizing the correlation filtering parameters. This is of great reference value for the preparation and output of entangled light fields in practical experiments.

In this paper, the Hermite-Gauss model TEM00 was treated as a signal light field, and a local light field composed of small displacement and balance homodyne detection system was studied. The experiment was carried out based on the system of sound frequencies (20 Hz to 20 kHz) transverse small displacement measurement. We discussed the shot noise of system, directivity noise and laser intensity noise effect on the displacement of the minimum detectable. According to the experimental results of noise measurement, when the SNR is 3 dB, the minimum measurable displacement at different frequencies in the sound frequency band is given, of which, the minimum measurable displacement at 1 kHz is 3×10－9?m, the minimum measurable displacement at 10 kHz is 1.2×10－10?m and the minimum measurable displacement at 15 kHz is 0.85×10－10?m. This paper lays a certain foundation for the experimental and theoretical research on the suppression of laser noise in acoustic frequency band and the reduction of directional noise in small displacement measurement system.

By using photon pairs generated from photonic crystal fiber, whose wavelengths can be continuously tuned from 750 nm～880 nm and 1 310 nm～1 620 nm, perform efficiency calibration for a single-photon detector (SPD) at multiple wavelengths covering three telecommands of O, C, and L we detected in the experiment. This method can be used for calibrating SPDs at any arbitrary wavelength in these three bands.

The information carried on the optical field was encoded to the time-bin qubit in the rubidium atomic band, and then the time-bin qubit was transmitted in the fiber for 2.3 km. The time-bin after transmission wasmeasured by the non-equilibrium Mach -Zehnder interferometer. The experimental results showed that the coherence retention of time-bin in the long distance transmission about one photon was 81%. Quantum network is a major research target in the field of quantum information. Scientists have tried to construct quantum networks using a variety of trapped ions, atoms, and quantum dots as nodes. Rubidium atoms of the alkali metal is a strong candidate for quantum nodes due to the good coherence and long coherent time of ground state spin waves. The entanglement of atomic spin wave and Stokes photon generated by spontaneous Raman process is very suitable for quantum network. The light - atomic quantum interface based on spontaneous Raman scattering has beendemonstrated experimentally. We have carried out an experimental research on the transmission of time-bin qubits in rubidium atomic band.

In order to improve the quality of fuzzy image reconstruction, improved quantum algorithm was proposed. Firstly, quantum information communication on different circles in the same ring was realized by virtual connection, which quantum information communication on different circles and other quantum information on the same ring was realized by using the virtual connection established previously. Secondly, self-checking process was achieved via quantum error correction. Thirdly, original image was estimated based on gradient norm; fuzzy kernel function was minimized based on auxiliary variable, Chau Laplace prior was used to restore image. Finally, the process was displayed elaborately. The simulation results showthat peak signal noise ratio of the improved quantum algorithm was improved 35.47%、42.58%、28.69%、23.39%、21.05%、14.28% comparing with IF、WF、GS、TVGS、CM、HLD, background suppress factor was improved 17.61%、22.41%、12.77%、8.48%、6.76%、6.17% comparing with IF、WF、GS、TVGS、CM、HLD, information entropy was improved 35.19%、42.27%、27.46%、19.15%、11.35%、6.31% comparing with IF、WF、GS、TVGS、CM、HLD, and average gradient was improved 58.23%、69.79%、47.33%、36.73%、27.55%、11.85% comparing with IF、WF、GS、TVGS、CM、HLD. It is better than other algorithms, while provides a new idea and method for fuzzy image restoration.

Quantum dense coding property of Heisenberg XYZ model with abundant interaction of various parameters in a time-varying magnetic field is studied in this paper. The evolution of channel capacity χ over time is simulated by Quantum State Diffusion Method (QSD). Numerical simulation shows that quantum dense coding depends on the environmental correlation coefficient γ, coupling coefficient J,Jz and the intensity B of cosine magnetic field. When the environment correlation coefficient γ variable small, that is, the non-Markov characteristic increases, the channel capacity χ of quantum dense coding obviously increases. Here it is worthwhile to propose that smaller coupling coefficients Jz, larger coupling coefficients J, and stronger time-varying magnetic field intensities B all are very useful for efficient quantum dense coding in this system, where it is very obvious in the case of non-markov, which is in turn very important for efficient information transmission.

A quantum system for the interaction of a two-mode coherent state field with V-type atom have been studied. The population and quantum entanglement of quantum systems were solved accurately without rotating-wave approximation. The effects of average photon number n- and atomic level superposition on the population and quantum entanglement were discussed, and the reasons of the non-rotational-wave terms transition affecting the dynamics of quantum systems were analyzed. The results show that the population and quantum entanglement evolution period increase with the increase of n-. The entanglement degree of the quantum system is smaller in the population collapse region and larger in the population recovery region. The initial value of quantum entanglement and the mean value decreases when the atom is in the superposition state at the initial time. The non-rotating-wave terms transition leads to a zigzag oscillation in the population and entanglement evolution curves.

In this paper, we choose 33Σ+1 as an intermediate state and obtain relevant vibrational spectra by scanning the frequency of PA laser. It is found that the production rate of ultracold 85Rb133Cs molecules in the lowest vibrational state, formed by short-range PA, is larger in 33Σ+1(v=3) than other vibrational states, the corresponding rotational constant in 33Σ+1(v=3) is abrupt and the energy is close to 23Π0－(v=14) state. All of these display the characteristic of resonant coupling between these two states. After the optimization of PA laser intensity and photoionization power, the production rate of 85Rb133Cs molecules in X1Σ+(v=0) is measured to be around 1.5×104/s. With the consideration of the parity of the molecular wave function and the selection rules,we find that 33Σ+1(v=3,J=1) intermediate state has the passway that can spontaneously decay to ground state of ultracold 85Rb133Cs molecules via single pass which is meaningful to explore on direct transfer from atom to molecule using stimulated Raman adiabatic passage.

Based on the nonlinear fractional Schrodinger equation (NLFSE), the optical modes in nonlinear PT symmetric waveguides and their stability are studied. Firstly, the optical modes in PT symmetric waveguides with fractional diffraction effects are given by using the square operator method. On this basis, the effects of fractional diffraction effect and non-Hermitian effect on the stability of these optical modes are studied by linear stability analysis method, andthe dynamics of linear stable and unstable optical modes are numerically simulated by using the stepwise Fourier method. The results show that there are ground states, first, second and third excited state optical modes in the fractional diffraction effect nonlinear PT symmetric system.

The magnetometer based on ensembles of NV centers has attracted much attention within the fields of quantum information. As a new technology, NV center magnetometer can detect magnetic field with high sensitivity and spatial resolution at room temperature, which has broad application prospects in the fields of weak magnetic field measurement. We expect the highest sensitivity to be achieved by any method; the factors affecting the sensitivity are the contrast and linewidth, which depend on the microwave (MW) and light powers; are critical for optimizing magnetometer sensitivity based on high-density nitrogen vacancy (NV) centers in diamond. In this paper, we report a study of the coherent population oscillation based on ensembles of NV centers by using two microwave channels to control quantum state of NV centers. The notion of coherent population oscillation is widely used in the atomic physics/quantum optics community but is essentially unknown in the EPR/ODMRcommunity. A home-made magnetic field detection system was set up to sense the external magnetic field and the experimental results of optically detected magnetic resonance show that the phenomenon of “hole burning” and the linewidth at the peak becomes narrower. We attribute the spectra to coherent population oscillations induced by the two nearly degenerate microwave fields. At the same time, because the sensitivity is related to the slope of signal modulation, the detected signal was demodulated with a lock-in amplifier referenced to the modulation frequency by a signal generator, the slope of microwave modulation signal increased from the experimental results. Under the condition of continuous wave experiment, both microwave channels are tuned to the resonance frequency between the ground state 3A2 of NV center ensembles, and the pump of one channel is set to a given frequency (ms=0ms=±1), and the probe is set to sweep frequency. In this experiment, we attribute the resonances occurring on the same transition to the coherent population oscillations (CPO) resulting from interference (beating) between two coherent electromagnetic fields (ms=0ms=+1). Via this method, the observed optically detected magnetic resonance spectra showed a complex narrow linewidth structure and whether the shape of the hole would change under different microwave conditions was tested. When the detection microwave power is constant, the lower the pump microwave power, the narrower the linewidth. When the pump microwave power is constant and the microwave frequency is changed, the hole burning always appears at the changed microwave frequency, and the effect occurs only for beat frequencies within the range determined by the population relaxation times. Finally, we modulated the optically detected magnetic resonance signal by using sine wave. Because the sensitivity of NV color center ensemble magnetic detection is inversely proportional to the maximum slope of demodulation curve, it is found that the modulation slope of coherent layout phenomenon was increased by 20%, which further improved the shot-noise-limited sensitivity of DC. This article is just a basic experiment about coherent population oscillation, however it has a good application for achieving high precision measurement in the future and provides a good support for reducing linewidth.